1. Field of the Invention
This invention relates generally to touchpads using surface capacitance technology. More specifically, the present invention is a new method of determining the position of a pointing object or objects on a surface capacitance touch panel.
2. Description of Related Art
Capacitive touch screens are readily available for use in diverse applications. As touch sensitive screens become more popular and more useful, the technologies to implement them are also evolving.
Several different touch screen and touchpad technologies have emerged including projected capacitance methods and surface capacitance methods. Projected capacitance methods are currently required to implement gestures that utilize more than one finger or pointing object on the surface at the same time.
For example, FIG. 1 is a top view of an array of orthogonal electrodes 6, such as a plurality of X (2) and Y (4) electrodes, which are often used in touchpad and touch screen technologies such as those produced by Cirque Corporation®. However, projected capacitance methods generally cost more to implement than surface capacitance methods because of the more intricate processes required to etch electrode patterns into a conductive surface.
An example of surface capacitance technology is shown in FIG. 2. Such a surface cap panel 10 is a solid sheet of a conductive material 16 disposed on an insulating substrate 18 such as glass, with sensors 12 disposed at the corners. The traditional method of measuring the position of a pointing object 14 or the “touch position” on the surface capacitance touch panel 10 is to apply an AC signal on all four corners of the touch panel's conductive layer 16. The conductive layer 16 can be made, for example, of Indium Tin Oxide (ITO).
To create the touch panel 10, the surface of the glass substrate 18 is flooded or covered with a substantially even layer of a resistive ITO material which forms a sheet resistance. A dielectric is then applied to cover the ITO conductive material.
After applying the AC signal to the conductive ITO material 16, the next step is to triangulate the touch position using the current flowing through each corner. It is common to apply either a sine wave or a square wave.
If an object such as a finger 14 comes in contact with the surface of the touch panel 10, a capacitor is formed between the ITO surface 16 and the finger tip 14. The capacitance value is very small, typically in the order of 50 pF. The amount of charge or current that has to be measured going into each corner 12 of the panel is therefore very small. Because the current is so small, the system is very susceptible to stray capacitance. Thus, the accuracy of touch panels 10 is often an issue.
With these two different touch technologies in mind, it is observed that software applications in portable and stationary electronic appliances such as computers, smart phones, and any other device that can use a touch interface, are now beginning to use a second point of contact (such as a finger and thumb or two fingers) to support gestures such as “pinch and zoom”, pan, rotate, etc. Other applications use a third simultaneous contact for a “next and previous” gesture, and even a fourth simultaneous contact for switching between applications.
Multi-finger gestures can also be accomplished using an “area gesture”, such as in the method taught by Cirque Corporation®, wherein multiple contacts are not tracked but instead the area gesture is accomplished by seeing the multiple contacts as only a single large object, where the multiple contacts only define the outer boundaries of the large object. The multiple points of contact can therefore be considered to have a height and a width.
Operating system software and Human Interface Device (HIG) standards are being modified to include these new gestures and methods of reporting multi-finger contact with a touch sensitive surface.
Unfortunately, it has not been possible to utilize the less expensive surface capacitance touch screens or touchpads (hereinafter to be referred to as “surface cap panels”) to support multi-finger gestures or area gestures because there has not been a suitable method available for tracking more than one point of contact or for determining the outer boundaries of a large object as defined by area gesture method of Cirque Corporation® for multiple points of contact. In other words, it has not been possible to determine height and width of a large object.
Accordingly, it would be an advantage over the state of the art to be able to utilize area gestures defined by multiple points of contact with surface cap panels that are being used as touch screens and as touchpads. Such a system would enable new multi-touch technology to be used with simpler touch screen and touchpad technology.